Effects of a Trumpet Mute Physics 193 Professor Steven Errede December 2010 By: Steven Kiebles 1 The trumpet is a versatile instrument that has been a mainstay of musical
ensembles since its most basic form, dating back to almost 1000 B.C. The modern
trumpet was perfected in the late 1800’s, and is now heavily utilized in various
types of musical genres, including rock, jazz, blues, and classical. The trumpet is
classified as a brass instrument, and plays in the key of B flat. A modern trumpet
generally has a mouthpiece on one end, and a bell on the other, with three valves
along the tubing that allow for the alteration of pitch. The trumpet also features a
slide attached to each valve, used to compensate for the intonation of certain notes.
The trumpet works like many musical instruments, the player uses his or her
mouth and air to create a standing wave in the trumpet, which comes out of the bell
and creates a difference in pressure. This pressure difference is perceived as sound
by the inner machinations of the human ear. The different frequencies that can be
emitted from the trumpet all pertain to a certain impedance value, measured in
ohms. This impedance at the bell end of the trumpet is reflected back through the
trumpet, which causes the players lips to buzz. This buzzing of the lips is what
allows the player to identify the frequency of the note.
A mute is an object that is placed in the bell of the trumpet to alter the sound
in some way. Various types of mutes, as well as various materials, can cause the
sound to be fuzzy, cause the trumpet to growl, or make the sound quieter. A straight
mute is the most common type of mute, and simply quiets the sound and makes it
fuzzier.
2 The trumpet in this experiment used was a Yamaha B flat trumpet, a very
basic model. The mute was a Harmon straight mute. The mouthpiece was a Bach
7C. When an instrument is a B flat instrument, this means that the tuning is
different from concert pitch. The notes on a B flat instrument are all one whole step
sharp from the notes of a C instrument, which is concert pitch. For example, if the
note played on a trumpet is written as C, it will have the same frequency as a B flat
on a piano or a guitar.
I studied the effects of an aluminum straight mute on a B flat trumpet at
various valve combinations. Specifically, I gathered and analyzed data on the effect
that the mute has on the impedance from the trumpet at various frequency. To
allow for more data to be analyzed, the experiment was performed with all three
valves down, all three valves up, and the first two valves down. This ensured that
the analysis was not altered by the valve combination. As opposed to the trumpet
actually being played, the standing wave was generated by a piezoelectric driver
placed at the mouthpiece. At the bell, there was a very small condenser microphone
that recorded the sound and data emitted from the bell. This is how all the data was
gathered for the experiment.
3 4 These pairs of graphs are all impedence, measured in ohms, versus
frequency, measured in hertz. In all of the pairs, the top graph is the trumpet
played without the straight mute in the ball. In the bottom graphs, the trumpet is
played with the mute in the bell. The vertical peaks in the graphs are known as
impedence peaks, and they occur at the frequencies at which notes can be played on
the trumpet. When these impedence peaks are higher, the notes are easier to play
Since higher notes need more air, they are more difficult to play, which is
represented in the graphs by the decreasing amplitude of the impedence peaks.
5 However, if you look at the impedence peaks of the trumpet with the mute,
and compare it to the same frequency without the mute, it is evident that the peaks
are significantly higher when the mute is in the bell. The difference in impedence
increases as the frequency increases towards the highest peak. After the highest
peak, the difference in impedence begins decreasing again. This is logical, and is
due to the fact that the lower notes and higher notes are harder to play and require
more air, which would not be significantly affected by the mute. The mute’s effect is
most pronounced at the highest impedence peak, which is a frequency of about 1000
hertz in the final pair of graphs. Based on the frequency and valve combination, this
note would be a C sharp written for trumpet. When transposed to concert pitch, it
would be a B. At this same frequency and valve combination, the impedence is
about 1000 ohms higher with the mute in the bell than it is without the mute. This
raised peak indicates that the mute does in fact increase impedence, and make the
note easier to play.
6 7 8 These inharmonicity plots show the inharmonicities, measured in ents, of
various notes played on the trumpet at various harmonics. The top graph is the
inharmonicities with the mute, while the bottom half is the inharmonicities without
it. You can see that the concert B flat and the G are lower with the mute than they
are without. This is a strange trend, as the mute should generally cause a note to go
sharp as opposed to flat. However, with the concert E flat, this trend is
followed,which is a strange discrepancy. Not only is the E flat higher with the mute,
it is almost 100 cents higher, or a whole semitone. These descrepancies suggest
some sort of error.
Overall, I believe this experiment was a success, as it was clearly evident
that the mute caused significant difference in the trumpet’s sound. The graphs
clearly display both the raised impedance peaks and the changes in
inharmonicities. If I were to repeat this experiment, I would gather data from a
recording of myself playing the trumpet in order to see if the inharmonicities would
change. I would also compare the effects of the straight mute to the effects of other
mutes, such as a cup mute or a harmon mute. Possible error in this experiment
could be due to the eventual loss of tuning of the trumpet. The trumpet was in the
box for several days, and over time it naturally goes out of tune. This could have
been the source of the seemingly innacurate data given by the inharmonicities.
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